Читать книгу Wine Faults and Flaws - Keith Grainger - Страница 73

Some older tasters, and wine writers, distinguish between the terms ‘aroma’ and ‘bouquet’. They use the term ‘aroma’ when referring to the primary aromas derived from the grapes. ‘Bouquet’ would encompass the assembled characteristics resulting from changes that have taken place during fermentation (secondary aromas), and particularly maturation and ageing (tertiary aromas). The distinction is far from clear‐cut, and as such, the words ‘aroma’ and ‘odour’ are used in this book as all‐encompassing terms.

There are some 800 or more volatile compounds that have been identified in wines, in concentrations ranging from a few nanogrammes to hundreds of milligrammes per litre. The olfactory perception thresholds of odorous compounds vary from 4 pg/l, to 100 mg/l, but the sensory threshold for any individual compound may differ when present with other compounds. It is even possible that some compounds may be detected at concentrations of a few femtogrammes per litre (fg/l).

There has been considerable research over the last couple of decades into the identification of the individual compounds (and their precursors) that contribute to wine aromas. These activities are still in their infancy. Table 2.3 lists some of the compounds contributing to individual aromas, including their origins and typical odour detection thresholds. The Sauvignon Blanc variety has been particularly well studied in respect of the precursors, development, and reactions of volatile thiols in the grapes, must, and wine, as reviewed in 2012 by Coetzee and du Toit [10]. The aromas commonly found in a young wine made from Sauvignon Blanc, and the volatile thiols that responsible for these aromas, are shown in Table 2.4.

Table 2.3 Some compounds responsible for wine aromas, their origins, aroma descriptors, and typical sensory detection thresholds.

Compound	Aroma descriptors	Sensory detection thresholda)
Primary aromas
Terpenes
Wine lactone	Lime, coconut, wood, sweat	10 ng/l
Linalool	Floral, rose, lavender ‘Muscat’ grape	25 μg/l
Geraniol	Geranium, rose, citronella	30–130 μg/l
Nerol	Rose	200–300 μg/l
α‐Terpineol	Lily of the Valley, spice	250–400 μg/l
Citonellol	Citronella	18–100 μg/l
Cis‐Rose oxide	Lychee, rose	100–200 ng/l
Trans‐rose oxide	Rose	80 μg/l
1,8‐Cineole (eucalyptol)	Eucalyptus	3.2 μg/l
N.B. Over 50 terpenes have been identified in grapes
Secondary (fermentation) aromas
Esters
Ethyl acetate	Pear drops, solvent, nail varnish remover (levels above 100 mg/l may regarded as a fault)	3.6–13 mg/l
Ethyl propanoate	Cherry	2.1 mg/l
Ethyl‐2‐Methylpropanoate	Strawberry, banana	1.8 mg/l
Ethyl hexanoate	Green apple, aniseed	14–140 μg/l
Ethyl octanoate	Meat fat	5 μg/l
Ethyl Decanoate	Floral, grape	200 μg/l – 1.5 mg/l
Ethyl butanoate (ethyl butyrate)	Pineapple	20–400 μg/l
Ethyl isovalerate	Fruits	3 μg/l
Isoamyl acetate	Banana	30 μg/l – 2.7 mg/l
Hexyl acetate	Pear	2.4 mg/l
Phenylethyl acetate	Rose, honey	250 μg/l – 6 mg/l
2‐Phenylethanol	Floral	20 mg/l
Alcohols
Ethanol	Alcohol!	100 mg/l
2‐Phenylethyl alcohol	Rose, lilac	14 mg/l
Isoamyl alcohol	Malted barley, Whisky	30 mg/l
1‐Hexanol	Cut grass	4.5 μg/l
Wood (maturation) aromas
2‐Furfurylthiol	Roasted coffee	4 pg/l
Furfural	Almond	20 mg/l
Eugenol	Clove, spice	500 μg/l
Trans‐Nonenal	Sawn wood	250 ng/l
cis/trans‐Whiskylactone	Coconut	125 μg/l
Guaicol	Smoke	75 μg/l
Vanillin	Vanilla	200–320 μg/l
Maltol	Caramel	30 μg/l

a) Sensory detection thresholds depend upon many criteria, including the presence of other compounds and the wine matrix. The figures stated have been extrapolated from numerous sources.

Table 2.4 Compounds contributing to the varietal aromas of Sauvignon Blanc wines.

Aroma	Thiol	Sensory detection thresholda)
Boxwood – broom, cat's pee	4‐Mercapto‐4‐methylpentan‐2‐one	0.8–3.3 ng/l
Citrus zest and peel	4‐Mercapto‐4‐methylpentan‐2‐ol	55 ng/l
Grapefruit, passion fruit	3‐Mercaptohexan‐1‐ol	60 ng/l
Mango, guava, passion fruit	3‐Mercaptohexyl acetate	4 ng/l
Cut grass	1‐hexanol	4.5 μg/l
Smoke, gunflint	Benzenemethanethiol	0.3 ng/l
Aroma	Methoxypyrazine	Sensory detection threshold a)
Green pepper, grass	2‐methoxy‐3‐isobutyl pyrazine (iBMP)	1–2 ng/l

a) Sensory detection thresholds depend upon many criteria, including the presence of other compounds and the wine matrix. The figures stated have been extrapolated from numerous sources.

It may sometimes be helpful for the taster to consider wine aromas in basic groups:

 Fruits (primary aromas);

 Flowers (primary aromas);

 Spices (primary, secondary, and tertiary aromas);

 Vegetables (primary and tertiary aromas);

 Oak aromas (secondary aromas);

 Other aromas.

Of course, it is possible to divide each of these basic groups into subgroups. For example, the fruits group might be divided into citrus, green, red, stone, and tropical fruits. Dried fruits may also be included. Each subgroup contains individual aromas and flavours.

All aromas detected during nosing should be noted, and when detailing individual descriptors, these may be linked to known varietal characteristics. For example, green apple, lime, peach, and mango are just some of the aromas that may be associated with Riesling. Strawberry, raspberry, red cherry, green leaf, and mushroom are typical aromas associated with Pinot Noir. The detection of any oak related aromas including vanilla, toast, nuts, and coconut may warrant interpretation (barrels/beans/chips?).